Your ball is the black one. Just click anywhere in the applet area, and the black ball begins to run towards the point you click. The initial velocity is proportional to the distance between the point you click and the black ball. The objective of the game is to drop all the balls except for the black one into the holes.
You can drag any one of the balls by holding down the shift key when all of the balls are standing still.
If you click the mouse button while holding down the control key, the black ball does not run, but instead, an orange line is drawn between the ball and the point you click. And the ball begins to run when you release the mouse button, if the control key is released first.
If you click mouse button while holding down the meta key, or you double-click, the black ball begins run at maximum velocity.